Homogenizing device for powdered solids which are not free flowing

ABSTRACT

AN HOURGLASS-SHAPED ASSEMBLY CONSISTS OF TWO CONICAL MIXING COMPARTMENTS SEPARATED BY A SCREEN. A DRIVEN SHAFT EXTENDS AXIALLY THROUGH THE ASSEMBLY AND IN EACH COMPARTMENT CARRIES AN AGITATOR AND A BRUSH, THE BRUSHES IN THE TWO COMPARTMENTS ENGAGING THE OPPOSITE SIDES OF THE SCREEN. IN ONE EMBODIMENT THE ASSEMBLY IS TILTABLE THROUGH 180* ABOUT A TRANSVERSE AXIS. IN ANOTHER EMBODIMENT TOW OR MORE ASSEMBLIES ARE CONNECTED TOGETHER IN SERIES AND SEPARATED BY   SCREENS ENGAGED BY ADDITIONAL BRUSHES. IN THE LATTER EMBODIMENT TILTING OF THE DEVICE IS UNNECESSARY.

United States Patent Inventor Elkan J. De Jong Rotterdam, Netherlands Apple No 742,072

Filed July 2,1968

Patented June 28, I971 Assignee Organon, Inc.

Orange, NJ.

Priority July 7. 1967 Netherlands 6709461 HOMOGENIZING DEVICE FOR POWDERED SOLIDS WHICH ARE NOT FREE FLOWING 6 Claims, 2 Drawing Figs.

u.s. Cl 259/64 lnt.Cl B0lf7/l8 Field of Search 259/2. 3, 4,

[56] References Cited UNITED STATES PATENTS 3,3 34,869 8/1967 Mukai 259/6X Primary Examiner- Edward L. Roberts Attorney-Kurt Kelman ABSTRACT: An hourglassshaped assembly consists of two conical mixing compartments separated by a screen. A driven shaft extends axially through the assembly and in each compartment carries an agitator and a brush, the brushes in the two compartments engaging the opposite sides of the screen. In one embodiment the assembly is tiltable through 180 about a transverse axis. In another embodiment two or more assemblies are connected together in series and separated by screens engaged by additional brushes. In the latter embodiment tilting of the device is unnecessary.

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ELKAN J. DE JONG AGENT HOMOGENIZING DEVICE FOR POWDERED SOLIDS WHICH ARE NOT FREE FLOWING The invention relates to a mixing and homogenizing device for powdered solids, at least one of which is not free flowing, combining the advantages of a batchwise operating mixer with those of a continuous mixer, with simultaneous elimination of the drawbacks of both types of mixer. The device is especially suited for mixing micronized materials, extremely finely divided powders.

There are many kinds of batchwise operating mixers for solids, hereinafter called batch mixers. A common feature of such mixers is that loading the components to be mixed and discharging the mixture obtained are effected discontinuously. Batch mixers include e.g. many kinds of tumbling mixers (double cone, cube, V and Y-mixers), mixers with agitators (planetary mixers, mixers with plows, knives, spiral helixes, kneading devices), ball mills, edge runner mills, ribbon mixers, etc.

Proportionately there are considerably fewer continuous mixers for solids. Often these are modified batch mixers. A common feature of these is that charging and discharging takes place continuously. Examples of continuous mixers are modified ball mills, edge runner mills and ribbon mixers, furthermore screw mixers and zigzag mixers.

In practice the choice between utilizing batch or continuous mixing is mainly governed by the quantity of material to be processed, continuous'mixing being best suited for large scale operations. In theory, however, it is preferable that choice of mixer should be based on the quality of mixing required and -not on throughput. For the sake of clarity here follows a review of the advantages and drawbacks of both types, expressly treating of mixtures of solids, at least one of the components of which is not free flowing.

A. Batch Mixers Advantages:

Simple dosing of components. Suitable for any quantity, large or small. Mixing time easy to control. Operation requires little skill. in general easily adaptable to circumstances deviating from the surroundings, such as temperature, pressure, exclusion of oxygen, or to operation under sterile conditions. Generally few space problems, especially with small mixers. comparatively inexpensive equipment.

Drawbacks:

Chance of dead spaces. No certainty that every quantity of material is mixed equally intensively. Waste of energy, because unmixed or not yet sufficiently mixed components and ready mixture are equally exposed to the mixing action. Consequently the mixing time is often lengthened, sometimes to the extent that the quality of the mixture deteriorates, even before the components are sufficiently uniformly distributed over each other. Generally the devices have an optimum charge, allowing of little deviation, neither upwards nor downwards.

'8. Continuous Mixers Advantages:

Suitable for very high output. Every quantity of material is equally intensively. mixed, the processed mixture is continuously removed. The mixing time (the dwelltime of the material to be processed in the mixing part of the apparatus) is often short. Less influence of dead spaces.

Drawbacks:

The uniformity of dosing the components is decisive for the quality of the mixture. in asmuch as the components or at least part thereof, are, as a matter of course, not free flowing. uniform dosing is difficult to realize and, therefore, expensive. On a small scale it is almost impracticable. Consequently this is the basis of the rule that continuous mixers can be used for solids which are not free flowing only with very large quantities. Also experiments with continuous mixers are expensive. Experiments with batch mixers are the only alternative, but, of

other, and the reverse. A device for mixing nonfree flowing solids, combining the advantages of both types and eliminating the drawbacks, would mark a distinct advance in the technology of mixing.

The essential characteristic of all continuous mixers is not the manner of charging and discharging, let alone the utility for large quantities. What is characteristic is that the material is fed as a whole through the mixing or homogenizing part. Consequently it is more correct to speak of a feed-through mixer than of a continuous mixer.

The device according to the invention is a feed-through mixer, a so-called continuous mixer for nonfree flowing, powdered materials. It can be used both continuously for large quantities and batchwise for small quantities. Up till now such a device has not been known.

The device is primarily characterized by at least one hourglass-shaped assembly of two conical mixing compartments, separated by a means such as a perforated plate or screen, and a driven shaft, passing axially and centrally through the assembly and supporting, in each compartment on either side of the said screen, at least one agitator rotating in the same direction and at least one rubbing means, e.g. a brush likewise rotating in the same direction and pressed against the said screen.

In a first embodiment this device is characterized by one hourglass-shaped assembly of two identical conical compartments, this assembly being adapted to tilt at least on a transverse axis at the level of the said screen. By tilting the assembly the mixing operation can be repeated.

The assembly can be suspended for tilting on a frame. On the sides away from the perforated plate or screen the mixing compartments can be provided with an at least partly transparent, removable lid.

Another possible embodiment of the device according to the invention is characterized in that a number of hourglassshaped assemblies is serially disposed on top of each other, the bottom of the lower compartment of each assembly connecting to the top of the upper compartment of the next assembly, with a screen placed inbetween on either side of which acts a rubbing means e.g. a brush. in this embodiment tilting is not necessary.

This embodiment of the device lends itself especially to processing larger quantities of material. Processing of such quantities in a tilting assembly would require a very heavy construction.

Measures which may be applied in both embodiments consist in that the rubbing means pressing on either side of the said perforated plate or screen are not disposed opposite each other, and that the driven shaft is adjustable in positions deviating in respect of the vertical, of course together with the whole device. The first measure results in a smooth feedthrough of the material through the perforated plate or screen, and the second measure gives a possibility to adjust the dwelltime of the mixture in each of the compartments.

The paddle gears or agitators can be mounted on a sleeve, slid on the central driven shaft and fixed in regard thereof. The agitators cover substantially the whole content of the compartments and may have a wide variety of shapes, they may e.g. be wire-, bladeor knife-shaped. Their shape can be selected so that the material in the compartments is shirled up or pressed downwards.

Also the rubbing means or brushes may differ in shape, and besides in material and consequently in hardness. They are secured either to an agitator or to a loose ring, slid on the central shaft and secured thereto. Agitators and rubbing means are exchangeable, the shaft being preferably driven variably by the motor and/or the gearing.

The device according to the invention has a hitherto unprecedented number of possibilities to control the intensity of mixing, in consequence of which the requirements as to quality can likewise be met in unprecedentedly efficient fashion.

Control and adjustment are possible with:

l. the number of revolutions per minute 2. the screen mesh size, along with the proportion between the sieve openings and the total surface of the screen, the latter being chiefly a matter of the materials and method of construction of the screen,

3. the agitator shape, which determines the effectiveness of premixing and aftermixing in the upper and lower compartment, respectively,

4. shape and material of the rubbing means; the brushes may be soft or hard, short haired or long haired, also a scraper ofe.g. Teflon may be used,

5. the inclination of the device, with: strong inclination the mixing time is, of course, considerably lengthened,

6. the number of passages, in said second embodiment determined by the number of assemblies.

For each mixture to be formed the optimum conditions can be selected, there often being an ample choice of possibilities. A definite quality of a mixture can be made e.g. with a fine mesh screen, a hard brush and a shaft inclination of 30 in two passages. The same quality could be attained with e.g. a screen of less fine mesh, vertically disposed shaft, but in four passages. It is important, especially for experiments, that the degree of charging scarcely plays a part, as opposed to many batch devices wherein a deviation from the optimum charge soon leads to decreased effectiveness.

With regard to the second embodiment of the device, described in the foregoing, it is observed that, naturally, the time during which the mixtures remains in the various compartments, are to be adjusted in respect of each other so that a regular feed-through is ensured, the screen mesh playing an important part. All this is to be determined empirically, with which one can the experience use with the tilting embodiment of the invention, which operates on the same lines. If with discontinuous charging the variation are not quite too great, a uniform mixture can be discharged continuously. The device can comprise fewer compartments.

Comparative experiments, covering mixtures of different composition, made with both a device according to the invention and commercially available devices, based on the most widely divergent constructions, showed that the former device is far superior.

In a device according to the present invention small quantities of liquid can be components of the material being mixed, if desired.

In the following operation and constructional details of the two embodiments of the device according to the invention will be elucidated with reference to the drawings. It is observed that the invention is not limited to these two embodiments, but includes all obvious variants.

FIG. 1 shows a longitudinal section of the tilting device.

FIG. 2 shows a longitudinal section of the nontilting device.

The components to be mixed are combined in the conical upper compartment A, whereupon the device is closed with lid 1 and subsequently motor 2 started.

This motor drives shaft 3 and the agitators 4 and brushes 5 rigidly secured thereto at a selected speed. The material is premixed by the upper agitator and conglomerates are rubbed an extra spreading takes lace.

When all the materia has passed the screen 6, 111 the embodiment'according to FIG. 1 the device is tilted on trunnions 8, journaled in a supporting frame 7. The motor 2 tilts with the device. Then the second compartment B is up and.

subsequently the material therein is stirred again and pressed through the screen. This operation can be repeated as often as is required to attain a satisfactory homogeneity. Through the sight glasses 9 in the lids 1 the progress can be watched. While an opening in each lid, which can be closed, may serve for drawing samples.

The embodiment in FIG. 2 has a number of hourglassshaped assemblies, serially disposed on top of each other. As appears from FIG. 2 the bottom of the lower compartment of each assembly connects to the top of the upper compartment of the assembly located thereunder, with a perforated plate or screen 10 disposed inbetween, on either side of which acts a rubbing means, e.g. a brush lll.

Deviating from what is shown in the drawings, the rubbing means may also extend diametrically across the whole screen, being disposed e.g. normal to the agitator.

I claim:

I. A mixing and homogenizing device for powdered solids at least one of which is not free flowing, comprising at least one hourglass-shaped assembly consisting of two conical mixing compartments, a screen separating said compartments, a driven shaft extending axially through said compartments, two agitators carried by and rotatable with said shaft in the respective compartments, and two rubbing means carried by and rotatable with the shaft in the respective compartments in pressing engagement with the opposite sides of said screen.

2. The device as defined in claim 1 wherein said two rubbing means are radially offset from each other.

3. The device as defined in claim 1 which is further characterized in that said assembly is adjustable angularly with respect to a vertical position of said shaft.

4. The device as defined in claim ll together with means mounting said assembly for tilting through at least 180 about a transverse axis passing substantially through the plane of said screen.

5. The device as defined in claim 1 together with at least one additional hourglass-shaped assembly of the same construction as the first-mentioned assembly connected vertically in series to the first-mentioned assembly with the lower compartment of one assembly communicating with the upper compartment of the other assembly, and an additional screen interposed between the communicating compartments of the two assemblies, and two additional rubbing means carried by and rotatable with said shaft in pressing engagement with the opposite sides of said additional screen.

6. The device as defined in claim 5 wherein said two additional rubbing means are radially offset from each other. 

